In an effort to detect and treat diseases, many physicians are using minimally invasive imaging techniques to view the internal body tissues of patients. Such techniques typically employ imaging devices such as video endoscopes, which are inserted into the patient and used to obtain images of the tissue. Such images are most commonly color images of reflected white light, where the image is composed of light from the entire visible spectrum. These images are typically displayed on a color video monitor.
A new imaging technique that may prove useful in detecting disease is one in which images are generated from a subset of wavelengths in the visible spectrum and, in particular, from blue and green wavelengths in the visible spectrum. In this imaging technique, tissue is illuminated with blue-green light which is preferentially absorbed by blood. As a consequence, superficial blood vessels appear dark in the resulting reflected light image. In addition, the blue-green light does not penetrate tissue and scatter as much as red light and, thereby, provides more detailed structural information about the tissue surface. Since the onset of diseases, such as cancer, are frequently accompanied by changes in tissue surface morphology and an increase in vascularity to support rapidly proliferating cells, such an imaging technique may be particularly useful in identifying early cancerous or precancerous lesions.
A conventional means of achieving such an imaging technique involves the use of specialized endoscopic light sources that are equipped with one or more filters to restrict the spectrum of illumination light to light in the blue-green wavelength band. However, because physicians often want to utilize both the full spectrum white light and the restricted spectrum, short wavelength imaging modes, such filters are generally incorporated into a mechanism which moves them into and out of the light path and thereby increases the cost and complexity of the light source. It is therefore desirable for an endoscopic imaging system not to require the incorporation and movement of filters to produce the light for the two different imaging modes, but still allow physicians to utilize the same light source for a full spectrum white light imaging mode and a restricted spectrum, short wavelength imaging mode.